Abstract
PsbP is a membrane-extrinsic subunit of photosystem II (PSII) and involved in retaining Ca2+ and Cl-, two inorganic cofactors for the water-splitting reaction. In previous study, a truncated PsbP lacking 19 N-terminal residues (Δ19) was found to bind to NaCl-washed PSII lacking PsbP and PsbQ without activation of oxygen evolution at all. Three-dimensional structure of PsbP suggests that deletion of 19 N-terminal residues would destabilize its protein structure, as indicated by the high sensitivity of Δ19 to trypsin digestion. The structure of PsbP also suggests that 15 N-terminal can be eliminated without affecting the entire protein structure. Thus, a series of truncated PsbP lacking 10-15 N-terminal residues (Δ10-15) were produced. Δ15 was resistant to trypsin digestion, suggesting that it retained core PsbP structure. Reconstitution experiments showed that Δ15 bound to NaCl-washed PSII membranes; however, it did not show the activation of oxygen evolution. Further analysis using PsbP Δ10-14 are undergoing.
